Water-swellable clays that have acceptable water-swellability and colloidal properties, e.g., the non-blue bentonites having a Fe.sup.+3 /Fe.sup.+2 ratio above 1.0, and preferably above 3.0, have a great number of industrial uses that rely upon the ability of the clay to absorb many times its weight in water. Such water-swellable clays, such as sodium bentonite, however, lose much of their absorbency if the water absorbed is contaminated with water-soluble metal salts of alkali metals or alkaline earth metals, particularly the sulfate or halide salts, such as sodium chloride, magnesium chloride, calcium bromide, calcium chloride, potassium chloride, salt-containing body fluids and the like. Some bentonite clays, such as the blue bentonites disclosed in Clem U.S. Pat. No. 2,672,442, require the uptake of calcium ions to provide acceptable water swellability and colloidal properties for industrial acceptance. The preferred water-swellable clays useful as starting materials in accordance with the present invention are non-blue bentonites (green to greenish yellow to yellow to cream colored) that have industrially acceptable water swellability and colloidal properties and have a Fe.sup.+3 /Fe.sup.+2 ratio greater than 1.0, preferably at least 3.0, and most preferably in the range of about 5.0 to about 15.0. Some of these industrial uses for the treated water-swellable clays of the present invention, where once dried water-swellable clays, e.g., sodium bentonite, have their absorbency adversely affected upon contact with salt-contaminated water, are described as follows.
1. Drilling Muds
In drilling wells by rotary methods it is a common practice to circulate, continuously, a drilling mud or fluid into and out of a borehole during the drilling operation. The drilling mud is pumped into a drill pipe from a mud pit and the mud passes down to the bottom of the borehole. The drilling mud then flows upwardly through an annular space between the borehole wall and the drill pipe, and finally flows from the borehole through a mud ditch back to the mud pit, wherein the mud is mechanically or chemically treated before recirculation through the borehole.
The drilling mud serves several purposes that influence such factors as the drilling rate, cost, efficiency and safety of the operation. The drilling mud lubricates and cools the drill bit, acts as a vehicle to carry the cuttings from the borehole, and provides sufficient equalizing hydrostatic pressure against the formation wall to prevent the borehole wall from cave-in during drilling. By using proper mud formulations, the borehole entry of gases and fluids encountered in the surrounding earthen formations pierced by the drill is inhibited and possible collapse or blowouts resulting from uncontrolled influxes of these formation fluids may be prevented. The drilling mud also exerts a "wall-building" effect whereby it often forms a thin filter cake on a borehole wall, thus sealing off the borehole and reducing water loss to the penetrated formations.
An acceptable mud must have body yet be free-flowing with relatively low viscosity in order to facilitate pumping. The mud must also have an acceptable gel strength in order to suspend solid material if circulation is interrupted and to prevent accumulation of solids at the drill bit to avoid mechanical jamming. Acceptable drilling muds may be either oil-based or water-based, and they are normally treated to provide the rheological properties that make them particularly desirable and useful for drilling wells. For example, drilling muds may be treated with barium sulfate (barite) or lead sulfide (galena) to increase their density.
The efficiency of the drilling process is related to the velocity of the mud flowing up the annular space between the borehole wall and drill pipe. This velocity is in turn related to the viscosity, density and flow properties of the mud. In addition, the drilling mud viscosity is known to depend upon the quality, concentration and state of dispersion of the colloidal solids of the mud. As the drilling operation proceeds, the rheological properties of the mud may be adversely affected by such factors as the nature of the drilled strata, loss or gain of water to the mud, chemically-active contaminants that may flocculate the mud, mud pH, and most importantly, the increasing temperatures and pressures encountered at deeper drilling depths. In order to maintain workable viscosities, the muds must be formulated to respond to varying circumstances and conditions encountered during use. Since improvements in efficiency are realized as the viscosity and density of a mud are increased, it is desirable to optimize drilling mud formulations to possess the highest viscosity and density workably feasible for a given formation at a given depth.
Whenever possible, usually for reasons of economy, water-based drilling muds are used throughout the drilling operation. The suspending solids in water-based drilling muds are typically clays from the kaolinite, montmorillonite or ilite groups. These clays impart desirable thixotropic properties to the drilling mud and also coat the walls of the well with a relatively impermeable sheath, commonly called a "filter cake", that retards fluid loss from the well into the formations penetrated by the well. These properties of the suspended, water-swellable clays are substantially adversely affected by contact of the clay with salt-contaminated water resulting in less clay swelling and concomitant lower viscosity and more fluid loss.
An exemplary montmorillonite clay that can be used in a water-base drilling mud is a non-blue bentonite. The bentonite is dispersed within the water-based liquid as colloidal particles and imparts various degrees of thixotropy to the drilling mud. Non-blue, e.g., sodium bentonite, water-swellable clays that are rewetted and redried, in accordance with the present invention, are initially non-blue clays, e.g., are initially industrially acceptable for this purpose, having good water swellability and colloidal properties and having a sufficient ratio of Fe.sup.+3 /Fe.sup.+2, at least above 1.0, preferably at least 3.0 and most preferably in the range of about 5.0 to about 15.0, and, after processing, have excellent rheological properties for use in preparing aqueous drilling muds despite contact with salt-contaminated water during the drilling process.
2. Lost Circulation Fluid
One difficultly often encountered in rotary drilling operations involves the loss of unacceptably large amounts of the drilling mud into a porous or cracked formation penetrated by the drill. The loss of drilling mud is termed "lost circulation", and the formation is termed a "lost circulation zone" or a "thief formation".
Lost circulation occurs when the well encounters a formation either having unusually high permeability or having naturally occurring fractures, fissures, porous sand formations, cracked or cavernous formations or other types of strata characterized by crevices, channels or similar types of openings conducive to drilling fluid loss. In addition, it is also possible for a formation to be fractured by the hydrostatic pressure of the drilling mud, particularly when a changeover is made to a relatively heavy mud in order to control high internal formation pressures.
When lost circulation occurs, the drilling mud pumped into the well through a drill string enters the cracks in a cracked formation or the interstices of a porous formation and escapes from the wellbore, therefore precluding return of the drilling mud to the surface. In the most severe situation, the lost circulation zone takes the drilling mud as fast as it is pumped into the wellbore, and, in the less severe situations, circulation of the drilling mud can be greatly reduced, and eventually result in a shutdown of drilling operations. Normally, the maximum amount of drilling mud loss that is tolerated before changing programs is approximately one barrel per hour. If a greater amount of drilling mud is lost, corrective measures are needed. Drilling generally is not resumed until the thief formation is closed off and circulation of the drilling mud reestablished.
The interruption of normal circulation prevents the removal, by entrainment, of cuttings and other materials from the borehole, leads to reduced hydrostatic pressure possibly followed by the influx into the wellbore of high pressure formation fluids, can result in the flooding of oil-producing zones with mud or the like, and may eventually cause the drill string to become stuck in the borehole. Even in situations where circulation is not completely lost and some drilling mud can return to the surface, the drilling mud flowing into the lost circulation zone must be replaced continuously. If the drilling mud loss is sufficiently high, the cost of continued drilling or well operation may become prohibitive. Therefore, the lost circulation of drilling mud is a condition that must be prevented or be corrected as quickly as possible.
The best method of controlling lost circulation is to conduct a drilling program such that mud loss will not occur. However, situations exist wherein even correct drilling techniques cannot avoid lost circulation. Therefore, many methods have been used in attempts to plug the cracks or interstices of lost circulation zones to prevent the escape of drilling muds. As a result, a wide variety of materials have been pumped into the well with the drilling mud in an effort to bridge or fill the cracks or interstices of thief formations. It has been found that some materials are successful under certain drilling conditions, yet the same material is unsuccessful under other drilling conditions.
One common method is to increase the viscosity of the drilling mud or to increase the resistance of the drilling mud to flow into the formation. Another technique involves the addition of a bulk material, such as cottonseed hulls, cork, sawdust, perlite, ground walnut shells, hay, wood shavings, granular plastic, vermiculite, rock, mica flakes, leather strips, beans, peas, rice, sponges, feathers, manure, fish scales, corn cobs, glass fiber, asphalt, ground tires, burlap or other fabrics to the drilling mud. By adding these fibrous, flaky or granular solids to the drilling mud and pumping the resulting mixture into the borehole, a bridge or mat forms over the cracks or interstices responsible for drilling mud escape.
Although lost circulation zones frequently are plugged by such bulk materials, successful plugging of the thief formation is not assured. Even if large volumes of a solids-containing drilling mud are pumped into the borehole, a bridge or mat may never form over the cracks or interstices of the thief formation. Moreover, the introduction of large quantities of a drilling mud containing a relatively high percentage of bulky solids can produce pressure surges that cause further fracturing and therefore result in additional fissures for even greater drilling mud losses. Bulk materials also have proven unsuccessful in sealing off porous formations because they have a tendency to deteriorate under the high drilling pressures, and therefore decrease in volume and become slimy so as to "worm" into the formation openings without forming an effective seal.
The water-swellable clays processed in accordance with the present invention are processed by starting with an industrially acceptable, e.g., non-blue, bentonite clay, that is initially industrially acceptable for this purpose, having good water swellability and colloidal properties and having a sufficient ratio of Fe.sup.+3 /Fe.sup.+2 above 1.0, preferably at least 3.0 and most preferably in the range of about 5.0 to about 15.0. The non-blue bentonite clay is rewetted and redried, as described in more detail hereinafter and, after processing, unexpectedly has the ability to continue to increase the viscosity of aqueous liquids, with time, so that the clay will continue to swell upon entering the interstices of a thief formation for effective plugging despite contact with salt-contaminated water during the drilling process.
3. Water Absorbency and Swellability
The water-swellable clays rewetted and redried in accordance with the principals of the present invention are capable of new and unexpected water-absorbency and swellability when contacted with salt-contaminated water making them very useful for a number of industrial products and processes. The water-swellable clays rewetted and redried in accordance with the principles of the present invention provide unexpected water absorbency of salt-contaminated water and swellability upon contact with salt-contaminated water making the clays very suitable for use in moisture impervious rigid and flexible panels; for preventing water contaminated with industrial waste, including metal salts, from seeping through soil containing one or more of the treated water-swellable clays; for water-proofing compositions in non-viscous sprayable forms, or paste or putty-like forms, capable of being applied by spray methods, caulking gun, or trowel; for use together with one or more elastomers and/or plasticizers for preventing the seepage of salt-contaminated water through the compositions; together with other additives such as xanthan gum and/or other gums for maintaining stability in salt-contaminated water; together with other components to manufacture a flexible grout composition for sealing drill holes contaminated with salt-contaminated water; for use as a water-swellable material in a layered water-sealing article of manufacture to prevent seepage of salt-contaminated water therethrough.
Examples of these technologies and uses for the water-swellable clays rewetted and redried in accordance with the present invention are disclosed in the following U.S. Patents, all of which are hereby incorporated by reference: Clem U.S. Pat. No. 3,186,896; Clem U.S. Pat. No. 4,048,373; Clem U.S. Pat. No. 4,021,402; Clem U.S. Pat. No. 4,084,382; Clem U.S. Pat. No. 4,087,365; Clem U.S. Pat. No. 4,279,547; McGroarty U.S. Pat. No. 4,316,833; Piepho U.S. Pat. No. 4,332,693; Harriett U.S. Pat. No. 4,534,925; Harriett U.S. Pat. No. 4,534,926; Alexander U.S. Pat. No. 4,634,538; Harriett U.S. Pat. No. 4,668,724; Harriett U.S. Pat. No. 4,696,698; Harriett U.S. Pat. No. 4,696,699; Alexander U.S. Pat. No. 4,886,550; Harriett U.S. Pat. No. 4,733,989; Alexander U.S. Pat. No. 4,832,793; Harriett U.S. Pat. No. 4,810,573; and Alexander U.S. Pat. No. 4,847,226.
Excellent gel strength is achieved when industrially acceptable, water swellable, non-blue starting clays are processed in accordance with the present invention and then hydrated in salt-contaminated water. The water-swellable clays processed in accordance with the present invention are non-blue, e.g., are initially industrially acceptable for gel strength, having good water swellability and colloidal properties and having a sufficient ratio of Fe.sup.+3 /Fe.sup.+2 above 1.0, preferably at least 3.0 and most preferably in the range of about 5.0 to about 15.0, and after processing by rewetting and redrying, the clays are excellent suspending agents for use in the cosmetics and pharmaceutical industries in amounts well know in the art.